mssql.class.php

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        $metac = $meta[$fieldname];
        $oldtype = strtolower($metac->type);
        $oldmetatype = column_type($xmldb_table->getName(), $fieldname);
        $oldlength = $metac->max_length;
        $olddecimals = empty($metac->scale) ? null : $metac->scale;
        $oldnotnull = empty($metac->not_null) ? false : $metac->not_null;
        $olddefault = empty($metac->has_default) ? null : strtok($metac->default_value, ':');

        $typechanged = true;  //By default, assume that the column type has changed
        $lengthchanged = true;  //By default, assume that the column length has changed

    /// Detect if we are changing the type of the column
        if (($xmldb_field->getType() == XMLDB_TYPE_INTEGER && substr($oldmetatype, 0, 1) == 'I') ||
            ($xmldb_field->getType() == XMLDB_TYPE_NUMBER  && $oldmetatype == 'N') ||
            ($xmldb_field->getType() == XMLDB_TYPE_FLOAT   && $oldmetatype == 'F') ||
            ($xmldb_field->getType() == XMLDB_TYPE_CHAR    && substr($oldmetatype, 0, 1) == 'C') ||
            ($xmldb_field->getType() == XMLDB_TYPE_TEXT    && substr($oldmetatype, 0, 1) == 'X') ||
            ($xmldb_field->getType() == XMLDB_TYPE_BINARY  && $oldmetatype == 'B')) {
            $typechanged = false;
        }

    /// Detect if we are changing the length of the column, not always necessary to drop defaults
    /// if only the length changes, but it's safe to do it always
        if ($xmldb_field->getLength() == $oldlength) {
            $lengthchanged = false;
        }

    /// If type or length have changed drop the default if exists
        if ($typechanged || $lengthchanged) {
            $results = $this->getDropDefaultSQL($xmldb_table, $xmldb_field);
        }

    /// Just prevent default clauses in this type of sentences for mssql and launch the parent one
        $this->alter_column_skip_default = true;
        $results = array_merge($results, parent::getAlterFieldSQL($xmldb_table, $xmldb_field)); // Call parent

    /// Finally, process the default clause to add it back if necessary
        if ($typechanged || $lengthchanged) {
            $results = array_merge($results, $this->getCreateDefaultSQL($xmldb_table, $xmldb_field));
        }

    /// Return results
        return $results;
    }

    /**
     * Given one XMLDBTable and one XMLDBField, return the SQL statements needded to modify the default of the field in the table
     */
    function getModifyDefaultSQL($xmldb_table, $xmldb_field) {
    /// MSSQL is a bit special with default constraints because it implements them as external constraints so
    /// normal ALTER TABLE ALTER COLUMN don't work to change defaults. Because this, we have this method overloaded here

        $results = array();

    /// Get the quoted name of the table and field
        $tablename = $this->getTableName($xmldb_table);
        $fieldname = $this->getEncQuoted($xmldb_field->getName());

    /// Decide if we are going to create/modify or to drop the default
        if ($xmldb_field->getDefault() === null) {
            $results = $this->getDropDefaultSQL($xmldb_table, $xmldb_field); //Drop but, under some circumptances, re-enable
            if ($this->getDefaultClause($xmldb_field)) { //If getDefaultClause() it must have one default, create it
                $results = array_merge($results, $this->getCreateDefaultSQL($xmldb_table, $xmldb_field)); //Create/modify
            }
        } else {
            $results = $this->getDropDefaultSQL($xmldb_table, $xmldb_field); //Drop (only if exists)
            $results = array_merge($results, $this->getCreateDefaultSQL($xmldb_table, $xmldb_field)); //Create/modify
        }

        return $results;
    }

    /**
     * Given one XMLDBTable and one XMLDBField, return the SQL statements needded to create its enum 
     * (usually invoked from getModifyEnumSQL()
     */
    function getCreateEnumSQL($xmldb_table, $xmldb_field) {
    /// All we have to do is to create the check constraint
        return array('ALTER TABLE ' . $this->getTableName($xmldb_table) .
                     ' ADD ' . $this->getEnumExtraSQL($xmldb_table, $xmldb_field));
    }

    /**
     * Given one XMLDBTable and one XMLDBField, return the SQL statements needded to drop its enum
     * (usually invoked from getModifyEnumSQL()
     */
    function getDropEnumSQL($xmldb_table, $xmldb_field) {
    /// Let's introspect to know the real name of the check constraint
        if ($check_constraints = $this->getCheckConstraintsFromDB($xmldb_table, $xmldb_field)) {
            $check_constraint = array_shift($check_constraints); /// Get the 1st (should be only one)
            $constraint_name = strtolower($check_constraint->name); /// Extract the REAL name
        /// All we have to do is to drop the check constraint
            return array('ALTER TABLE ' . $this->getTableName($xmldb_table) .
                     ' DROP CONSTRAINT ' . $constraint_name);
        } else { /// Constraint not found. Nothing to do
            return array();
        }
    }

    /**
     * Given one XMLDBTable and one XMLDBField, return the SQL statements needded to create its default 
     * (usually invoked from getModifyDefaultSQL()
     */
    function getCreateDefaultSQL($xmldb_table, $xmldb_field) {
    /// MSSQL is a bit special and it requires the corresponding DEFAULT CONSTRAINT to be dropped

        $results = array();

    /// Get the quoted name of the table and field
        $tablename = $this->getTableName($xmldb_table);
        $fieldname = $this->getEncQuoted($xmldb_field->getName());

    /// Now, check if, with the current field attributes, we have to build one default
        if ($default_clause = $this->getDefaultClause($xmldb_field)) {
        /// We need to build the default (Moodle) default, so do it
            $results[] = 'ALTER TABLE ' . $tablename . ' ADD' . $default_clause . ' FOR ' . $fieldname;
        }

        return $results;
    }

    /**
     * Given one XMLDBTable and one XMLDBField, return the SQL statements needded to drop its default 
     * (usually invoked from getModifyDefaultSQL()
     */
    function getDropDefaultSQL($xmldb_table, $xmldb_field) {
    /// MSSQL is a bit special and it requires the corresponding DEFAULT CONSTRAINT to be dropped

        $results = array();

    /// Get the quoted name of the table and field
        $tablename = $this->getTableName($xmldb_table);
        $fieldname = $this->getEncQuoted($xmldb_field->getName());

    /// Look for the default contraint and, if found, drop it
        if ($defaultname = $this->getDefaultConstraintName($xmldb_table, $xmldb_field)) {
            $results[] = 'ALTER TABLE ' . $tablename . ' DROP CONSTRAINT ' . $defaultname;
        } 

        return $results;
    }

    /**
     * Given one XMLDBTable and one XMLDBField, returns the name of its default constraint in DB
     * or false if not found
     * This function should be considered internal and never used outside from generator
     */
    function getDefaultConstraintName($xmldb_table, $xmldb_field) {

    /// Get the quoted name of the table and field
        $tablename = $this->getTableName($xmldb_table);
        $fieldname = $this->getEncQuoted($xmldb_field->getName());

    /// Look for any default constraint in this field and drop it
        if ($default = get_record_sql("SELECT id, object_name(cdefault) AS defaultconstraint
                                         FROM syscolumns
                                        WHERE id = object_id('{$tablename}')
                                          AND name = '{$fieldname}'")) {
            return $default->defaultconstraint;
        } else {
            return false;
        }
    }

    /**
     * Given one XMLDBTable returns one array with all the check constrainsts
     * in the table (fetched from DB)
     * Optionally the function allows one xmldb_field to be specified in
     * order to return only the check constraints belonging to one field.
     * Each element contains the name of the constraint and its description
     * If no check constraints are found, returns an empty array
     */
    function getCheckConstraintsFromDB($xmldb_table, $xmldb_field = null) {

        $results = array();

        $tablename = $this->getTableName($xmldb_table);

        if ($constraints = get_records_sql("SELECT o.name, c.text AS description
                                            FROM sysobjects o,
                                                 sysobjects p,
                                                 syscomments c
                                           WHERE p.id = o.parent_obj
                                             AND o.id = c.id
                                             AND o.xtype = 'C'
                                             AND p.name = '{$tablename}'")) {
            foreach ($constraints as $constraint) {
                $results[$constraint->name] = $constraint;
            }
        }

    /// Filter by the required field if specified
        if ($xmldb_field) {
            $filtered_results = array();
            $filter = $xmldb_field->getName();
        /// Lets clean a bit each constraint description, looking for the filtered field
            foreach ($results as $key => $result) {
                $description = trim(preg_replace('/[\(\)]/', '',  $result->description));   // Parenthesis out & trim
                /// description starts by [$filter] assume it's a constraint beloging to the field
                if (preg_match("/^\[{$filter}\]/i", $description)) {
                    $filtered_results[$key] = $result;
                }
            }
        /// Assign filtered results to the final results array
            $results =  $filtered_results;
        }

        return $results;
    }

    /**
     * Given one object name and it's type (pk, uk, fk, ck, ix, uix, seq, trg)
     * return if such name is currently in use (true) or no (false)
     * (invoked from getNameForObject()
     */
    function isNameInUse($object_name, $type, $table_name) {
        switch($type) {
            case 'seq':
            case 'trg':
            case 'pk':
            case 'uk':
            case 'fk':
            case 'ck':
                if ($check = get_records_sql("SELECT name 
                                              FROM sysobjects 
                                              WHERE lower(name) = '" . strtolower($object_name) . "'")) {
                    return true;
                }
                break;
            case 'ix':
            case 'uix':
                if ($check = get_records_sql("SELECT name 
                                              FROM sysindexes
                                              WHERE lower(name) = '" . strtolower($object_name) . "'")) {
                    return true;
                }
                break;
        }
        return false; //No name in use found
    }

    /**
     * Returns an array of reserved words (lowercase) for this DB
     */
    function getReservedWords() {
    /// This file contains the reserved words for MSSQL databases
    /// from http://msdn2.microsoft.com/en-us/library/ms189822.aspx
        $reserved_words = array (
            'add', 'all', 'alter', 'and', 'any', 'as', 'asc', 'authorization',
            'avg', 'backup', 'begin', 'between', 'break', 'browse', 'bulk',
            'by', 'cascade', 'case', 'check', 'checkpoint', 'close', 'clustered',
            'coalesce', 'collate', 'column', 'commit', 'committed', 'compute',
            'confirm', 'constraint', 'contains', 'containstable', 'continue',
            'controlrow', 'convert', 'count', 'create', 'cross', 'current',
            'current_date', 'current_time', 'current_timestamp', 'current_user',
            'cursor', 'database', 'dbcc', 'deallocate', 'declare', 'default', 'delete',
            'deny', 'desc', 'disk', 'distinct', 'distributed', 'double', 'drop', 'dummy',
            'dump', 'else', 'end', 'errlvl', 'errorexit', 'escape', 'except', 'exec',
            'execute', 'exists', 'exit', 'external', 'fetch', 'file', 'fillfactor', 'floppy',
            'for', 'foreign', 'freetext', 'freetexttable', 'from', 'full', 'function',
            'goto', 'grant', 'group', 'having', 'holdlock', 'identity', 'identitycol',
            'identity_insert', 'if', 'in', 'index', 'inner', 'insert', 'intersect', 'into',
            'is', 'isolation', 'join', 'key', 'kill', 'left', 'level', 'like', 'lineno',
            'load', 'max', 'min', 'mirrorexit', 'national', 'nocheck', 'nonclustered',
            'not', 'null', 'nullif', 'of', 'off', 'offsets', 'on', 'once', 'only', 'open',
            'opendatasource', 'openquery', 'openrowset', 'openxml', 'option', 'or', 'order',
            'outer', 'over', 'percent', 'perm', 'permanent', 'pipe', 'pivot', 'plan', 'precision',
            'prepare', 'primary', 'print', 'privileges', 'proc', 'procedure', 'processexit',
            'public', 'raiserror', 'read', 'readtext', 'reconfigure', 'references',
            'repeatable', 'replication', 'restore', 'restrict', 'return', 'revoke',
            'right', 'rollback', 'rowcount', 'rowguidcol', 'rule', 'save', 'schema',
            'select', 'serializable', 'session_user', 'set', 'setuser', 'shutdown', 'some',
            'statistics', 'sum', 'system_user', 'table', 'tape', 'temp', 'temporary',
            'textsize', 'then', 'to', 'top', 'tran', 'transaction', 'trigger', 'truncate',
            'tsequal', 'uncommitted', 'union', 'unique', 'update', 'updatetext', 'use',
            'user', 'values', 'varying', 'view', 'waitfor', 'when', 'where', 'while',
            'with', 'work', 'writetext'
        );
        return $reserved_words;
    }
}

?>